Chronic orofacial pain affects 10% of Americans and there currently is no effective treatment. The most common and most severe forms of orofacial pain include head and neck cancer pain, TMJ pain and masticatory muscle pain. The primary functional problem for orofacial pain patients is pain with chewing. However, there is no animal behavioral assay that quantifies the impact of nociception on oral function and that parallels the symptoms of patients. We hypothesize that chronic orofacial pain produces quantifiable masticatory changes. Moreover, we hypothesize that reduced gnawing function can be used as a measure of nociception. To test these hypotheses we have designed, custom built and pilot tested a novel device that objectively measures gnawing function in rodents. In this project we will use our novel device to quantify significant impairment of gnawing function in animal models of head and neck cancer pain, TMJ pain and masticatory muscle pain. To confirm that the altered gnawing function in the three models is secondary to pain we will demonstrate reversal with agents used clinically to treat these forms of chronic pain. We anticipate that our work will contribute fundamentally to improved understanding of nociceptive mechanisms of the trigeminal system by providing a quantitative functional nociceptive assay that does not depend on subjective behavioral interpretation and does not require observational time by an investigator. [unreadable] [unreadable] [unreadable]